Electric furnace.



W. 1. WRIGHTON.

ELECTRIC FURNACE.

APPucArloN FILED 1:11.19, 1915.

1, 165,055. Patented Dec. 21, 1915.

2 SHEETS-SHEET l. 5 HQ- .1 It

l 11155.. 1, Iv ,j i i i W. J. WRIGHTON.

ELECTRIC FURNACE'.

APPLICATION FILED FEB. I9, 1915.

UNITED sTATEs PATENT oEEIoE.

WILLIAM J. WBIGHTON, 0F PHILADELPHIA,'PENNSYLVANIA, ASSIGNOR TO THE v LEEDS & NORTHRUP COMPANY, 0F PHILADELPHIA, PENNSYLVANIA, A CORPO- :aATroN or PENNSYLVANIA.

ELECTRIC FUR'NACE.

Specification of Letters Patent.y

Patented Dec. 21, 1915.

Application led February 19, 1.915. Serial No. 9,223.

T o all whom t may concern: l

Be it known that LWILLIAMJ. iVmGHToN, a citizen of the United States, residing in the city of Philadelphia,y county of Philadelphia, and State of Pennsylvania, have in- `vented a new and useful Electric Furnace, of which the following is a specification.

My invention relates to electric furnaces in which heat is produced by the passage of electric current through a resistance conductor embedded in a refractory substantially non-electrically conducting material.

My invention resides in an electric heater comprising a resistance conductor or wire embeddedv in a refractory substantially nonelectrically conducting material which has relatively good or high heat conductivity and whose co-efiicient of expansion is substantially equal to or differs so ylittle from that of the resistance conductor that under v great variations' in temperature the conductor and refractory material maintain their relative positions without ydamage to either.l

My invention resides also in a heater of the character referred to to which there is applied a mass or coating of refractory substantially non-electrically conducting material which has lower heat conductivity than the refractory material in which the conductor is embedded and which is joined thereto and has substantially the same coefficient of expansion; this mass or coating of refractory material reduces heat losses, lends mechanical strength to the heater element or unit and, being intimately united with the refractory material embedding the vconductor and having substantially the same 'co-efficient of expansion there 1s no tendency for these refractory-materials to break apart or separate due to great temperature changes.

My invention resides also in the method of producing a heater element.

My invention resides 1n the features of heater construction and of furnace construction hereinafter described and defined in the claims.

For an illustration of one of the forms my invention may take and of means for practising my method reference' is to be had to the accompanying drawings, in which:

Figure 1 is a vertical sectional view,partly in elevation, of a heater embodying my invention. Fig. 2 is a horizontal sectional view taken on the line X-X of Fig. 1. Fig. 3 is a side elevational view, partially in section, of a form employed in making the heater. Fig. 4; is an end elevational View of the same with one of the end flanges removed. Fig. 5 is a fragmentary cross sectional view, on larger scale, through the form and heater unit. Fig. 6 is a fragmentary view illustrating part of the Winding form. Fig. 7 is a vertical sectional view, parts in elevation, showing a furnace employing the heater unit, together with a diagram of an arrangement of electric circuits which may be employed.

The heater H comprises ythe resistance conductor 1, of any suitable material, such as Excello or other wire of nickel-chromium alloy, disposed or Wound in any suitable .manner and embedded 1n a layer or mass 2 -eicient of expansion of the conductor l'that through the wide ranges of temperature involved the material 2 will not separate from the conductor 1 or crackof therefrom, The material for the layer 2 which I have found to yield satisfactory results is alundum powder or cement, U on the layer 2 is formed the layerft of a p astic materi l, which has no or verylsmall electrical con uctivity and whose heat conductivity is much less than that of the material 2 to prevent, so far as possible, the loss of heat in an outward direction. The material f1: preferably has a coefiicient of expansion e ual to or differing so little from that of t e material 2 that through the wide range of temperatures paratively porous structure that it assumes on hardening or drying. At the ends of the unit the mass 4 is formed into the flange 5, lending strength and rigidity to the unit and serving as means for confining or sup-` porting "the conducting leads connecting with the resistance conductor 1.

rlhe resistance conductor 1 may be disposed asa single winding, or, as later described, may be disposed as two separate windings, one of which consists of a single conductor 1 and the other of two conductors 1 in parallel with each other for procuring different heating effects. The common terminal for the two heater windings is represented at 6 and extends'from the winding 1 through the materials .2 and 4 and extends through the insulator bushing 7 inthe lower flange 5. The other terminals of the two heater windings are at the top of the heater H, one of them being connected to the lead 8 extending downwardly through the short superposed tubular insulators 9, and thence through a perforation in the lower flange 5, which perforation may have an insulating bushing like bushing 7. The terminal of the other heater-winding is connected to a lead similar to lead 8 at the top of the cylinder and extends downwardly outside ythereof and thence through the lower dange 5, such lead being indicated at 10, Fig. 2, and is disposed in short tubular insulators 11 similar to insulators 9. v i

TWhere the lead 8 passes the lower end o the heater winding the full difference of potential exists between the lower end of the heater windings and the conductor 8,

and to prevent substantialcurrent leakage through the materials 2 and 4 at this region `there may be molded in thematerial a piece of mica or other suitable extremely highly refractory vmaterial 12.

The nature of the material of the conductor 1 may be such that it will become coated with an oxid due to the action of oxygen on the conductor 1; and such oxid, particularly when the conductor 1 is a nickelchromium alloy, serves to prevent occurrence of any fusion into or with the material 2.

For producing a heater such as H apparatus illustrated in Figs. 3 to 6 may be employed. lnner members 13 and 14, in the shape of channels or half boxes, form the support for the corner pieces 15 upon whose faces 16 are disposed the edges of the strips meenam 17 which extend through slots in the end flanges 18 detachably secured to pieces 15. When the parts have been thus far assembled the key member 19 is forced between the members 13 and 14, separating them, thereby transmitting a spreading action through the members 15 to the strips 17 whose outward movement is limited by the ends of the slots in the end flanges or plates 18.

As seen in Fig. 6 the outer edge of each of the strips 17 may be notched as indicated at 17a to receive the conductor 1. Topthe bracket 20 may be secured one end of the conductor 1 and the form is then rotated and the eonductoiguided into the notches 17 of the strips 17 in succession so that theconductor 1 is wound, in the example illustrated, into what may be termed a helix, and its other end secured to bracket 20a. When a double heater winding is provided as hereinbefore referred to, the first, fourth, seventh, etc., strands 21 are the successive turns of the'resistance winding consisting of a single conductor 1, the intermediate strands 22 being the two strands of the other heater winding.

When the conductor 1 has abeen wound upon the form, the wet cement or material 2 is applied between the strands of the heater conductor to the outer surfaces of the members 13, 14 and 15, the heater conductor 1 being spaced from the surfaces of these members by the distance from the bottom of the slot 17, Fig. 6, to the lower edge 23.0f the strip 17. rThis distance determines the thickness of the material 2 from the heating conducto-r to the inner surface of the chamber 3. The plastic material 2 is applied until a suitable depth is reached outside of the conductor 1. While the material 2 is still moist or plastic the material 4 is applied When the layer 2 has been completed the strips 24 are removed and the spaces formerly occupied by strips 24 are filled in with material 2. With the layer 2 thus completed a strip 25, Fig. 5, is placed upon the layer 2 and serves as a guide for the depthv to which the material 4 is to be applied. When this -layer 4 has been completed, the strips 25 are removed and the spaces formerly occupied by them are lled with the material 4. The material is now allowed to dry or set and when suitably firm, the flanges 18 are removed, the key 19 removed,l whereupon the members 13 and 14 release the members 15, and all these meinbersand strips 17 are withdrawn, leaving the heating unit H with By the employment of a furnace heater of the character above described furnace temperatures of 1,800 degrees Fahrenheit, more or less, are available; and at such temperature neither the resistance conductor 1 nor the material 2 is fluxed; and at such temperature and all lower temperatures there is no luxing action between the refractory material 2 and the material of the conductor 1, and the material 2 maintains its solidity and form and its mechanical. strength for suitably holding and retaining the resistance conductor. And at such temperatures the material 2 and the outer material 4 of lower heat conductivity maintain their bond and union with each other.

In Fig. 7 is shown a form of furnace and appurtenances, the furnace having a heater such as H. Suitable legs or standards 26, shown as angle irons, have their upper ends secured together by suitable angle irons 28 which receive and support the furnace F. The member 27, as of asbestos board, is secured tolegs 26 and serves to carry the terminals 38, 39 and 40. The furnace F comprises the metal casing 29 having at its lower end the angle irons 30 to which is secured the asbestos board 31 upon which are secured the angle irons 32 at the lower endof the inner furnace casing-33, also preferably of sheet metal. Between the casings 29 and 33 may be a packing of any material 34 of poor heat conductivity. In the bottom of the casing 33 are disposed the asbestos air cell boards 35 affording high insulation against heat/transfer downwardly. Upon the air cell boards 35 is disposed a fire brick 36 upon which rests the heater H. The space between the heater H and the inside of the casing 33 may be filled with material 37 of poor heat conductivity, such as magnesium carbonate. On the asbestos board 27 are the bindingposts 38, 39 and 40. The post 39 is connected to the common lead 6 of the heater conductors; to the binding post 38is connected the other terminal of the double winding heater coil; and to the binding post 40 is connected the other terminal of the single heaterl coil. The leads 6, 8 and 10 extend from the heater H through holes in the fire brick 36, air cell boards 37 and the asbestos board 31.

Resting on the fire brick 36 within the heater chamben 3 isa tube 41, as of alundum, upon which may rest the material to receive the heat treatment. The upper end of the tube 41 is slotted at 42 to allow entry of the conductors 43 and' 44 forming a thermojunction T which may contact with the ma'- -means of the thermo-couple T and terial receiving the heat treatment. The conductors 43 and 44 are of any suitable dissimilar materials to form a thermo-junction.

Resting upon the top of the heater H are two fire bricks 45, one not shown in Fig. 7, each provided with a slot 46 and a handle 47. Between the two fire bricks the conductors 43 and 44 extend upwardly from the chamber 3. The slots 46 of the two lire bricks register with each other forming an aperture for which a suitable cover may be provided and through which the interior of the chamber 3 may be viewed. l

'Against the casing 29 lie the brackets 48 upon .the lateral feet 49 extending downwardly from the bottom of the sheet metal member 50 across whose top extends a sheet metal plate 51 around whose edge is secured the angle iron 52. The member 51 forms a table which rests" by the feet' 49 upon the ledges 48. The table 51 has a hole registering with the upper end of the casing Secured to the casing 29 are the angle irons 53 to which is secured the vertical board 54 of asbestos or other insulating material upon which may be disposed the electrical control apparatus. On the board 54 may be disposed the instrument 55 connected in circuit with the thermo-junction T whose component-s 43 and 44 extend to the binding posts 56 and /57 from which conductors 43 and 44 of like materials extend to the instrument 55. If the temperature variations at the instrument 55 are found'to be so great as to introduce serious errors the instrument 55 will be located at any other suitable point. By

the instrument 55 heat conditions within the furnace chamber 3 may be noted.

Gk is a suitable source of electric current which communicates through the switch 58 with the two line terminals 59 and 60 on the switch board 54. From the terminal 59 extends a conductor 61 to the binding post 39 to the common terminal of the two resistance windings ofthe unit H. From the conducconnects with the remaining terminal of the vsingle coil heater resistance.

R is a rheostat whose one terminal connects by conductor with. the switch terminal 7() and whose other adjustable terminal or contact 71 connects through conductor 72 with the switch terminal 63. vThe switch 73 is radapted to connect the switch terminal with the switch terminal 7 4 or the switch terminal 7 5, of which 7 is' connected by conductor 76 with the switch terminal-69 while the terminal 75 is connected by conductor 77 with the switch terminal 65.

L is a. pilot electric lamp whose termlnals are connected to the main terminals 59 and 60, and serves as an indicator that the line switch 58 is closed.

Upon closure of the line switch 58, and with the switch 64 closed and switch 68 open, current will flow from terminal 60 through ammeter 62, switch 64, conductor 66, through the low resistance or double coil of the heater H, thence through conductor 61 to the other line terminal 59, thus energizing the low resistance heating coil. `With the switch 68 in the closed position and switch 64 open current will flow from terminal 60 through ammeter 62, switch 68, conductor 78 through the single resistance coil, thence through conductor 61 to the other main terminal 59. When both of these switches 64 and 68 are closed a maximum amount of energy' is passed through the heater H, which energy is converted into heat which is conducted into the chamber 3 to raise the temperature therein.

lVith the switches 64 and 68 open, and thev switch 73 closedin engagement with terminal 74, current will flow from the line terminal 60 through the ammeter 62, through conductor 72, rheostat R, switch terminal 70, switch 73, switch terminal 74:, conductor 76, conductor 78 through the single resistance coil of the heater H and by return conductor 61 to the main terminal 59. This brings the rheostat R into series with the single resistance coil and the current therein may be adjusted by adjusting the contact 71. By throwing the switch 73 over to its other position in engagement with terminal 75, the rheostat R is thrown into series with the double resistance coil of the heater H.

What I claim is:

1. The method of making a tubular electric heating element, which consists inwinding a resistance conductor upon and at a distance from a removable form having a surface corresponding with the inner surface of the tubular element, applying plastic material around said conductor and against said form, whereby said conductor is embedded in said`material at a distance from said surface, and allowing said plastic material to set.

2. The method of making a heating ele- -ment, which consists in supporting a resistance conductor upon and at a distance from a removable form, applying plastic material around said conductor and against said form, allowing said plastic material to set, and thereafter removing the form.

3. The method of making a heating element, which consists in supporting a resist- Licence ance conductor'npon and at adistance from a removable form, applying plastic material around said conductor and against said form, while said material is plastic applying thereto and merging therewith plastic material of different nature, allowing said plastic materials to set, and thereafter removing the form.

4. An electric furnace heating element for producing a temperature of approximatelyy y1800 degrees F. comprising a resistance conductor embedded in non-vitreous plastic refractory material, said material and said conductor having substantially equal coeflicients of expansion at and below said temA perature.

5. An electric furnace heating element for producing a temperature of approximately 1800 degrees F., comprising a resistance conductor embedded in non-vitreous plastic refractorymaterial of relatively high heat conductivity forming a wall of the furnace fire chamber, said material and said conductor having substantially equal co-eiiicients of expansion at arid below said temperature. i

6. An electric furnace heating element comprising a resistance conductor embedded inplastic refractory material forming a wall of a fire chamber, said material and said conductor having substantially equal coefficients of expansion, and a coating of plastic refractory material merged with said first named material and having lower heat conductivity.

7.` An electric furnace heating element comprising a resistance conductor embedded in plastic refractory material forming a wall of a fire chamber, said material and said conductor having substantially equal coefficients of expansion, and a coating of plastic refractory material merging with said first named material, said materials having substantially equal co-eiiicients of expansion.

8. An electric furnace heating element having a ire chamber wall of alundum cement, a resistance conductor embedded Vin said cement near the inner surface thereof, and a material of lower heat conductivity than said cement merged therewith and disposed thereon.

9. An electric furnace heating element having a fire chamber wall of alundum cement, a resistance conductor embedded in said cement near the inner surface thereof, and a relatively porous coating of low heat .conductivity of a mixture of clay and asbestos fiber merged with and disposed upon said cement.

10.11 hollow heating element having a wall of plastic refractory material, a resistance conductor embedded in said material near the inner surface thereof, said material and said conductor having substantially equal. cti-efficients of expansion, and an outer coating of plastic refractory material merged with said first named plastic material and having lower heat conductivity.

1l. A hollow heating element having a wall of plastic refractory material, a resistance conductor embedded in said material near the inner surface thereof, said material and said conductor having substantially equal coefficients of expansion, and an outer coating of plastic refractory material merged with said first named material and having substantially equal co-eilicients of expansion.

l2. [i tubular heating element comprising a mass of plastic refractory material forming the inner Wall thereof, a resistance conductor embedded in said material near the inner surface thereof, an outer coating of plastic refractory material merged with said first named material and having lower heat conductivity.

13. A tubular heating element comprising a mass of plastic refractory material forming the inner Wall thereof, a resistance conductor embedded in said material near the inner surface thereof., an outer coating of plastic refractory material merged With said first named material and having lower heat conductivit and a flange on the end of said plastic material.

I4. A tubular heating element comprising a mass of plastic refractory material form ing the inner Wall thereof, a resistance conductor embedded in said material'near the inner surface thereof, an outer coating of inner surface thereof, an outer coating of plastic refractory material merged With said first named material and having lower heat conductivity, a flange on the end of said plastic material, a lead to said resistance conductor extending 'through said flange,

and a member of highly refractory material embedded in said plastic material between said conductor and said lead.

In testimony whereof I have hereunto affixed my signature in the presence of the two subscribing witnesses.

WILLIAM J. WRIGHTON. Witnesses:

NELLE Freni), Anios S. MARSH. 

